This invention relates to devices for measuring gas flow rates and in particular to in-line gas flow rate sensors and to systems utilizing such sensors.
In a propane gas system where the gas consumers are supplied propane gas from a propane tank supply, a float level sensor is used in the propane tank to monitor the propane gas level. In such systems, the user periodically views the tank level sensor and then requests delivery of replacement propane gas as required. While such fuel level sensors which are mounted in the tank can provide a reliable indication of the gas level remaining in the tank, they are difficult to maintain and time-consuming to repair when needed in view of their placement within the tank itself.
It is therefore desired to provide a propane tank level monitoring system which can not only sense and display the level of gas in the propane tank, but which can also provide a signal to a central location to use the information to track gas usage rate and to schedule delivery of replacement fuel as needed. In particular, it is desired to provide an in-line gas flow rate sensor for sensing the gas flow rate from which the level of the propane gas remaining in the tank can be derived.
In accordance with the principles of the present invention, there is provided an in-line gas flow rate sensor using a Hall effect sensor responding to changing magnetic flux corresponding to changing gas flow rates to produce an output signal representing changes in the gas flow rate.
In particular, there is provided a gas flow rate sensor which includes a flow tube, a diaphragm member movably mounted in the flow tube and which has a central aperture for receiving the gas flow. A tapered plug is mounted in the flow tube with a free plug end projecting within the central aperture of the diaphragm member. A spring has one end fixed in the flow tube and a movable end in contact with the diaphragm member to resiliently urge the diaphragm member into contact with one end of the tapered plug corresponding to a central aperture closed position. In response to increasing gas rates, the diaphragm member is moved along the tapered plug away from the central aperture closed position and towards the free plug end.
A magnet is fixed to the movable diaphragm member for slidable movement within the flow tube to respond to increasing gas flow rates and thereby provide a changing magnetic flux, and a magnetic flux sensor is mounted adjacent the magnet for responding to the changing magnetic flux and thereby producing an output signal for presenting changes in the gas flow rate.
The tapered plug includes a plug outer surface shaped to provide a linear relationship between the magnetic flux density and the output of the magnetic sensor. Thus, as the diaphragm member containing the magnet is moved for instance from an initial flow tube orifice closed position on the tapered plug to an orifice opened position with respect to the tapered plug in response to an increased gas flow rate, the output of the magnetic sensor follows in a linear relationship from the orifice closed to the orifice opened position. The output of the magnetic sensor thereby provides a signal indication which can be utilized in a known manner to provide the gas flow rate.
The flow rate sensor includes a pressure sensor for sensing the gas pressure at the inlet of the flow tube and a temperature sensor for indicating the temperature of the gas. Using a well known algorithm, such as the Universal Gas Sizing Equation, with the values of the gas pressure, temperature, output signal from the magnetic sensor, and known physical parameters of the flow rate sensor, the gas flow rate can be obtained. Accordingly, starting with a known full gas tank level and having determined the gas flow rate exiting the tank, the actual level of gas remaining in the tank can readily be determined. This information can conveniently be utilized for scheduling delivery of replacement fuel to the tank.